In recent years, introduction of a shared channel such as DSCH (Downlink Shared CHannel) used by a plurality of communication terminals (users) has been studied to transmit a large amount of packet data over the downlink. For example, when transmission is performed using DSCH, on a dedicated channel, each user transmits control data, performs transmission power control and maintains synchronization, while receiving information indicating a transmitted DSCH signal is to the user and information on transmission rate of DSCH signal.
In DSCH transmission, scheduling as to determine users and their priority to transmission data is performed corresponding to the downlink quality. For example, a base station monitors downlink qualities for all the users under control of the base station, and preferentially assigns DSCH to users providing higher quality. A terminal obtains CIR (Carrier to Interference Ratio) based on a CPICH (Common PIlot CHannel) signal, and notifies the base station of the CIR information, whereby the base station is capable of monitoring the downlink quality.
Further, selection of MCS (Modulation and Coding Scheme) is performed corresponding to the downlink quality. Also in this case, a terminal obtains CIR based on a CPICH signal, and notifies the base station of the CIR information, whereby the base station is capable of selecting a scheme.
However, when performing the scheduling and MCS selection based on CIR obtained from a CPICH signal in a terminal, the terminal should notify CIR. It is thus necessary for the terminal to always transmit CIR for the scheduling and MCS selection. Therefore, a problem arises that information to be transmitted using uplink signals is increased.